HSTest.cs

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace HSTest
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            hs_init(IntPtr.Zero, IntPtr.Zero);
        }

        [DllImport("formatter.so", CallingConvention = CallingConvention.Cdecl)]
        private static extern void hs_init(IntPtr argc, IntPtr argv);

        [DllImport("formatter.so", CallingConvention = CallingConvention.Cdecl)]
        private static extern void hs_exit();

        [DllImport("formatter.so", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
        private static extern IntPtr format(string original);

        private void button1_Click(object sender, EventArgs e)
        {
                textBox2.Text = Marshal.PtrToStringAnsi(format(textBox1.Text));
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            hs_exit();
        }
    }
}